In order to increase the energy density and power of lithium ion batteries, attempts have been made to use metal materials, such as silicon, germanium, tin, and zinc, alloying with lithium and oxides of these metals as negative electrode active materials instead of carbonaceous materials such as graphite.
Lithium released from a positive electrode active material is absorbed into a negative electrode active material made of a metal material alloying with lithium or oxides of these metals during initial charge. All the lithium cannot be extracted during discharge and an indefinite amount of the lithium is retained in the negative electrode active material, thereby causing irreversible capacity. Patent Literature 1 below discloses a nonaqueous electrolyte secondary battery in which a film containing a metallic lithium powder is formed on a negative electrode for the purpose of compensating for irreversible capacity.